Piezoelectric component and method for producing a piezoelectric component

ABSTRACT

A method for producing a piezoelectric component is disclosed. In an embodiment, the method includes producing a ceramic precursor material of the general formula Pb 1-x-y-(2a-b)/2 V (2a-b)/2 ″Ba x Sr y [(Ti z Zr 1-z ) 1-a-b W a RE b ]O 3 , where RE is a rare earth metal and V″ is a Pb vacancy, mixing the ceramic precursor material with a sintering aid, forming a stack which includes alternating layers including the ceramic precursor material and a layer including Cu and debindering and sintering the stack thereby forming the piezoelectric component having Cu electrodes and at least one piezoelectric ceramic layer including Pb 1-x-y-[(2a-b)/2]-p/2 V [(2a-b)/2-p/2] ″Cu p Ba x Sr y [(Ti z Zr 1-z ) 1-a-b W a RE b ]O 3 , where 0≤x≤0.035, 0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009, 0.009≤b≤0.011, and 2a&gt;b, p≤2a−b.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. application Ser. No.14/241,400, filed May 7, 2014 and issued as U.S. Pat. No. 9,570,669,which is a national phase filing under section 371 of PCT/EP2012/064538,filed Jul. 24, 2012, which claims the priority of German patentapplication 10 2011 112 008.8, filed Aug. 30, 2011, each of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

A piezoelectric component and a method for producing a piezoelectriccomponent are specified.

BACKGROUND

Piezoelectric components such as piezoelectric multilayer components areused, for example, as actuators in fuel injection systems.

SUMMARY

At least one embodiment of the invention provides a piezoelectriccomponent having improved properties. At least one further embodiment ofthe invention provides a method for producing a piezoelectric componenthaving improved properties.

A piezoelectric component is specified that has at least onepiezoelectric ceramic layer and at least one electrode adjacent thepiezoelectric ceramic layer, the piezoelectric ceramic layer having apiezoelectric ceramic material of the general formulaPb_(1-x-y-[(2a-b)/2]-p/2)V_([(2a-b)/2-p/2])″Cu_(p)Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃.In this formula 0≤x≤0.035, 0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009,0.009≤b≤0.011, 2a>b, p≤2a-b, RE is a rare earth metal, and V″ is a Pbvacancy.

A component of this kind may have one electrode each, for example, onboth sides of the piezoelectric ceramic layer. Alternatively thecomponent may also be a multilayer component comprising at least two,preferably at least 100 piezoelectric ceramic layers. In this case theelectrodes adjacent the piezoelectric ceramic layers are internalelectrodes, with one internal electrode each being disposed between twoceramic layers. A multilayer component of this kind may additionallyhave opposing outer faces on each of which an external electrode isapplied. The external electrodes are produced from the same material asthe internal electrodes or have a different material from the internalelectrodes. The internal electrodes are then divided into two groups,with one group of internal electrodes being contacted with one externalelectrode, and the other group of internal electrodes being contactedwith the other external electrode.

The piezoelectric ceramic material is a ceramic based on lead zirconatetitanate (PZT) of the general formula ABO₃ or Pb(Zr_(1-z)Ti_(z))O₃, andtherefore has a perovskite structure. PZT ceramics have what is called amorphotropic phase boundary of two coexisting ferroelectric phases, atetragonal phase and a rhombohedral phase. This PZT ceramic is doped atits B sites with W as donor and with a rare earth metal RE as acceptorand, for x>0 and/or y>0, is doped at the A sites with Ba and/or Sr. Thedoping with Ba and/or Sr may result in a lowering of the Curietemperature of the ceramic material. W may be present in the VIoxidation state. Furthermore, at A sites, the ceramic material has Cucations, which may be present in particular in the I oxidation state. Inthe ceramic material, during its production, the Cu acts as acceptorand, during sintering, produces temporary oxygen vacancies, leading tostable piezoelectric properties on the part of the piezoelectriccomponent. Stable piezoelectric properties may be brought about, forexample, by sufficiently dense piezoelectric ceramic materials (forexample, ≥96% of the theoretical density) and by large grain growth(with an average grain size of, for example, ≥2 μm or ≥3 μm).

In multilayer components, advantageous piezoelectric properties may bedependent on the mobility of the displacement of ferroelectric domainwalls in the PZT ceramic in an electrical field. The lower the densityof the grain boundaries in the volume of the ceramic, or the greater theextent to which grain growth comes about up to an optimum average grainsize in the sinter densification process, the less the restriction onthe mobility. In PZT ceramics, grain growth may be promoted by theacceptor-induced formation of oxygen vacancies.

Furthermore, a combined donor-acceptor doping at the B sites, in otherwords doping with W and RE, may bring about an increase in theconcentration of the vacancies V″, governed by the incorporation of REacceptor centers. At the same time, during sintering, a correspondinglyhigh concentration of oxygen vacancies, V_(O), may be induced. With adoping concept of this kind, owing to the increased defectconcentration, sufficient sinter densification of the piezoelectricceramic may be achieved at temperatures of as low as about 950° C., andthe grain growth that is essential for the development of advantageouspiezoelectric properties may be considerably increased. Thedonor-acceptor ratio here may be set such as to produce a slight excessof vacancies at A sites in the finished ceramic. The oxygen vacancyconcentration induced by RE centers during sintering is then no longerpresent in the finished ceramic.

Partial occupation of the vacancies may come about through Cu acceptorsat the A sites, thereby further promoting grain growth.

In PZT ceramics there may be the following substitutions: Pb^(II) at theA sites may be substituted by a cation of higher valence, this beingreferred to as a positive defect (since now a positive charge islocalized more at the A site), thereby inducing the formation of anegatively charged defect (electron donor). Neutralization takes placeeither by formation of Ti^(III) at a B site, or by formation of avacancy at an adjacent Pb″ or A site, as for example, V″/2 (tripledefect). Furthermore, Pb″ at the A sites may be substituted by a cationof lower valence, this being referred to as a negative defect, since nowa positive charge is localized less at the A site, thereby inducing theformation of a positively charged defect (electron acceptor).Neutralization takes place by formation of a vacancy at an oxygen siteV_(O)″, as for example, V_(O)″/2 (triple defect). V_(O)″ may be occupiedby ½ O₂, then forms 2 O and hence defect electron states in the oxygenvalence band, with acceptor effect, which blocks harmful electronconduction.

(Ti/Zr)^(IV) at the B sites may be substituted by a cation of highervalency, this being referred to as a defect, since now a positive chargeis localized more at the B site, thereby inducing the formation of anegatively charged defect (electron donor). Neutralization takes placeeither by formation of Ti^(III) at a B site or by formation of a vacancyat an adjacent Pb^(II) or A site, as for example, V″/2 (triple defect).Furthermore, (Ti/Zr)^(IV) may be substituted at the B sites by a cationof lower valency, this being referred to as a defect, since now apositive charge is localized less at the B site, thereby inducing theformation of a positively charged defect (electron acceptor).Neutralization takes place by formation of a vacancy at an oxygen siteV_(O)″, as for example, V_(O)″/2 (triple defect). V_(O)″ may be occupiedby ½ O₂, then forms 2 O and thus defect electron states in the oxygenvalance band, with acceptor effect, and this blocks harmful electronconduction.

Through combined donor/acceptor doping it is equally possible to achieveneutralization, with donors or acceptors remaining according to whichcomponent is predominant.

The rare earth metal RE may be selected from a group which encompassesLu, Yb, Tm, Er, Y, Ho, and Dy. According to one embodiment, the rearearth metal is Yb. It may be present in the III oxidation state in theabovementioned piezoelectric ceramic material.

The at least one electrode may comprise or consist of Cu. The componentis therefore, for example, a piezoelectric multilayer component with Cuinternal electrodes. The use of Cu electrodes or Cu internal electrodesis more cost effective by comparison with conventional electrodes,consisting, for example, of the noble metals Ag/Pd, and this is a factorparticularly with multilayer components.

According to one embodiment, the piezoelectric ceramic material may bePb_(0.9451)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃. This ceramic material has a high density of, forexample, 97.3% to 97.5% of the theoretical density, and a large grainsize of 2 to 3 μm. The dielectric constant ε is 2100 and the couplingfactor k_(p) is 0.65. This ceramic material therefore has advantageouspiezoelectric properties.

Further specified is a method for producing a piezoelectric component.The method comprises the method steps of A) producing a ceramicprecursor material of the general formulaPb_(1-x-y-(2a-b)/2)V_((2a-b)/2)″Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃,B) mixing the ceramic precursor material with a sintering aid, C)forming a stack which has in alternation a layer comprising the ceramicprecursor material and a layer comprising Cu, D) debindering andsintering the stack, with formation of a component having Cu electrodesand at least one piezoelectric ceramic layer which comprisesPb_(1-x-y-[(2a-b)/2]-p/2)V_([(2a-b)/2-p/2)]″Cu_(p)Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃where 0≤x≤0.035, 0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009, 0.009≤b≤0.011,2a>b, p≤2a-b, RE is a rare earth metal, and V″ is a Pb vacancy.

“In alternation” in relation to the stack formed in method step C) mayalso mean that a layer comprising Cu is not applied to each layercomprising ceramic precursor material. For example, certain layerscomprising ceramic precursor material may be disposed one atop another,with no layers comprising Cu between them. The stack formed has at leastone layer comprising the ceramic precursor material, and two layerscomprising Cu, disposed on opposite sides of the layer. The term “stack”includes an arrangement of more than two, more particularly more than100 layers comprising ceramic precursor material, with layers comprisingCu disposed between them. A stack of this kind is formed into amultilayer component having internal Cu electrodes in method step D).

With the method it is possible, for example, to produce a componentaccording to the versions above. The “layer” in method step C) maycomprehend compression moldings and films. From films it is possible,for example, to form a multilayer component.

The method therefore allows doping with W and a rare earth metal RE atthe B sites of a PZT ceramic with perovskite structure, and also theincorporation of Cu acceptor centers at the A sites. The doping at the Bsites already gives rise to high efficacy in the development of defects,and hence the contraction, i.e., the sinter densification, and anincreased grain growth during sintering. Through the additionalincorporation of the Cu acceptor centers it is also possible with themethod, using inexpensive Cu electrodes, to produce components whichfeature high performance.

According to one embodiment, method step A) may have the followingsteps: A1) providing a mixture of starting materials which are selectedfrom a group which encompasses Pb₃O₄, TiO₂, ZrO₂, WO₃, RE₂O₃, BaCO₃ andSrCO₃, A2) calcining the mixture at a first temperature and milling themixture to a first average diameter, A3) calcining the mixture at asecond temperature which is higher than the first temperature.

In method step A), therefore, by means of a mixed oxide method, aceramic precursor material of the general formulaPb_(1-x-y-(2a-b)/2)V_((2a-b)/2)″Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃is produced, according to the desired stoichiometric composition, withthe indices being selected from 0≤x≤0.035, 0≤y≤0.025, 0.42≤z≤0.5,0.0045≤a≤0.009, 0.009≤b≤0.011, and 2a>b. RE₂O₃ may be, for example,Yb₂O₃, Lu₂O₃, Tm₂O₃, Er₂O₃, Ho₂O₃, Dy₂O₃ or Y₂O₃. Where BaCO₃ and/orSrCO₃ is also added to the mixture, it is possible thereby to achieve alowering of the Curie temperature of the ceramic in the finishedcomponent.

In method steps A2) and A3), the oxide components can be reacted in twocalcination steps with milling in between, leading to the formation of aPZT ceramic powder which is particularly homogeneous in relation to theformulation. In method step A2), the oxide components mixed in methodstep A1) can be reacted at a first temperature selected from the 850° C.to 925° C. range. The reaction may take place after the components, forexample, have been mixed in an aqueous slip by means of ZrO₂ grindingmedia, the water has been removed by evaporation, and the mixture hasbeen sieved. The duration of the reaction may be 2 hours, for example.The product obtained is subsequently milled to a first average diameterd₅₀, which may be selected to be smaller than 1 μm. For this purpose,the product may first be slurried in water.

In method step A3), the mixture obtained in method step A2) may bereacted a second time, at—for example—a second temperature, which may beselected from the 930° C. to 970° C. range. The duration of thisreaction may be 2 hours, for example. For this purpose, the mixtureobtained in method step A2) may first be evaporated down and sieved.

It is therefore possible in method step A) itself, in which a two-stagecalcination with milling in between is carried out, to obtain apulverulent ceramic precursor material having substantially uniformdistribution of the components in the perovskite structure of the PZTceramic.

According to one development, in method step B), PbO or Pb₃O₄ may beadded as a sintering aid. Pb₃O₄ may undergo conversion on heating fromas low as 500° C. into PbO, with elimination of oxygen. The fractionselected for the sintering aid may be between 0.5 and 3 mol %, moreparticularly between 0.5 and 2 mol %, based on 1 mol of ceramicprecursor material. The actual sintering aid PbO may therefore be addedin the form of Pb₃O₄ to the mixture obtained in method step A). From atemperature of about 890° C. onward, the added PbO forms a melt, as aresult of which mechanisms of liquid phase sintering are manifested,which kinetically promote grain growth and contraction. Because thesintering aid is not added to the oxide mixture in method step A), butis only admixed after the synthesis of the property-bearing PZT ceramicprecursor, the addition of the sintering aid is defined and controlledand hence the application of the sintering aid is improved. As a result,uncontrolled, partial elimination of PbO due to evaporation and reactionwith firing aids during calcination can be avoided. The sintering aid istherefore able to be effective in the sinter densification process inline with the amount specifically employed.

Simultaneously with, before, or after the addition of the sintering aid,it is possible in method step B) for the mixture obtained in method stepA) to be milled to a second average diameter which is smaller than thefirst average diameter. This may be an operation of fine milling, whichmay further promote the sintering activity. For this purpose, themixture, in other words the reaction product from method step A), may bemilled in an aqueous slurry or in a nonaqueous medium such as ethanol,using ZrO₂ beads having a diameter of ≤0.8 mm. The second averagediameter d₅₀ may be selected from the range <0.4 μm, more particularlyfrom the 0.3 μm to 0.35 μm range. As a result, a high specific surfaceenergy can be obtained, and the resultant sintering activity can beutilized for the development of an optimum ceramic microstructure atabout 1000° C. to 1050° C., more particularly at 1000° C. to 1010° C.,in the presence of Cu electrodes. The combination of high specificsurface energy and the donor-acceptor doping at the B sites mayeffectively activate the resulting driving force for sinterdensification.

According to a further embodiment, in method step B), additionally, Cu₂Omay be added, with a fraction of 0.05 to 0.1 mol %, corresponding to thefraction p in the general formula. In this way, Cu acceptor centers canbe generated in the PZT ceramic at the A sites, and these centers,during sintering, additionally induce oxygen vacancies and therebypromote sinter densification and grain growth. In this way it is alsopossible to promote the advantageous piezoelectric properties. The Cu₂Ocan be added to the mixture which has already been finely milled to thesecond average diameter, or to a slip produced from the finely milledpowder.

The finely divided powder obtained in method step B) may be convertedinto granules after a binder has been added. The granules can be used inturn to provide compression moldings in slice form or a slip forproducing ceramic films. To produce a slip, an aqueous or nonaqueousdispersing medium, butyl acetate, for example, may be employed incombination with suitable dispersants and binders.

In method step C), furthermore, the layer comprising the ceramicprecursor material may be sputter-coated with Cu or printed with a Cupaste. If the layer comprising the ceramic precursor material is acompression molding, it may be sputter-coated with Cu, for example. Ifthe layer is a film, it may be printed with Cu paste, for example.

According to one development, in method step D), debindering may takeplace under steam with exclusion of oxygen. In this case, above about400° C., the low oxygen partial pressure resulting from the thermaldecomposition of steam may be lowered further by controlled supply ofoxygen gas (forming gas). Debindering is carried out before sintering,in order to eliminate the organic constituents first of all. This may becarried out at temperatures of up to 550° C. In a process known ashydroreforming, with formation of H₂ and CO₂, the residual carboncontent can be reduced to less than 300 ppm. Binders based onpolyurethanes, for example, may be particularly suitable for debinderingby means of steam in the absence of air, on the basis of theirhydrolytic cleavage into monomers. The low residual carbon content afterdebindering reduces the risk of oxidation of Cu and/or the reduction ofPb by organic constituents.

The sintering in method step D) may take place at an oxygen partialpressure which lies between the equilibrium partial pressure of PbO/Pband the equilibrium partial pressure of Cu/Cu₂O. In this case the oxygenpartial pressure may be set by a mixture of steam and forming gas.Accordingly there is a steam-hydrogen atmosphere whose composition, forthe processing window between the equilibrium oxygen partial pressure ofPbO/Pb and that of Cu/Cu₂O, can be calculated from tabulatedthermodynamic data as a function of the temperature, and leads, at 1000°C., for example, to an oxygen partial pressure of around 10⁻⁷. Thesetting of the oxygen partial pressure may therefore be set individuallyfor the respective temperature. Which oxygen partial pressure can beemployed at which temperature may be calculated from thermodynamic dataand monitored by an oxygen probe.

Through the application of an oxygen partial pressure which is betweenthe equilibrium partial pressure of PbO/Pb (or PbTiO₃/Pb,TiO₂) and theequilibrium partial pressure of Cu/Cu₂O, and which can be settemperature-dependently, it is possible to prevent oxidation of Cu toCu₂O and reduction of PbO to Pb and/or of PbTiO₃ to Pb and TiO₂. At thesame time, W^(VI) and Yb^(III) may be redox-stable under suchconditions, and therefore not subject to reduction. Accordingly, W^(VI)and Yb^(III) may indirectly become fully active as defects, in theirfunction of promoting sinter densification and grain growth, as a resultof temporary development of vacancies.

The sintering in method step D) may take place at a temperature selectedfrom the 1000 to 1050° C. range, more particularly from the 1000 to1010° C. range. For this purpose, the stack may be heated at a heatingrate of about 3 K/min to 1000° C. to 1050° C., more particularly to1010° C., and maintained for a number of hours, 3 hours for example. Thecooling may take place more slowly than the heating.

As a result of the debindering and sintering being carried out under theaforementioned operating conditions, the ceramic precursor materialwhich is sintered to give the doped PZT ceramic may take up minoramounts of Cu from the electrodes, present in the I oxidation state, atthe vacancies of the A sites. “Minor amounts” may mean, for example,about 600 ppm, corresponding to 0.003 mol of Cu based on 1 mol of PZTceramic. At the sintering temperature, these Cu acceptor centersadditionally induce oxygen vacancies and thereby promote sinterdensification and grain growth. This effect can be boosted by theabovementioned, optional addition of Cu₂O in method step B).

It is possible accordingly to produce a piezoelectric ceramic whichcomprisesPb_(1-x-y-[(2a-b)/2]-p/2)V_([(2a-b)/2-p/2])″Cu_(p)Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃where the following is the case: where it is the case that 0≤x≤0.035,0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009, 0.009≤b≤0.011, 2a>b and p≤2a-b.

With the method, therefore, a component featuring enhanced performancecan be produced. This is accomplished through the incorporation of Cuacceptors and through the defined addition of a sintering aid for sinterdensification and development of a sufficiently coarse grainmicrostructure with not very many grain boundaries in the volume of theceramic. The driving force for sinter densification, resulting from thespecific surface energy through fine milling and the donor-acceptordoping at B sites, may be effectively activated by mechanisms of liquidphase sintering, governed kinetically.

With the method it is possible, for example, to sinter stacks of severalhundred ceramic layers with Cu electrodes disposed between them, thesestacks being thereby densified and, in a subsequent step, singularized.In this way it is possible to produce actuators, for example.

According to one embodiment, in the method it is possible to selectx=0.0295, y=0.0211, Z=0.475, a=0.00753, b=0.0095 and RE=Yb, and so inmethod step D) at least one piezoelectric ceramic layer comprisingPb_(0.9451)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃ is produced. This ceramic material has enhancedpiezoelectric properties, such as a high density, high deflectionparameters, and a large average grain diameter.

Using light or electron microscopy and also radiography, the propertiesof the sintered compression moldings or films produced by the method canbe characterized in terms of their density and their microstructure. Thedielectric and piezoelectric properties can be determined by means ofdeflection and resonance measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the specified component and the method, and their advantageousembodiments, are elucidated by means of figures, which are schematic andnot true to scale, and also by a working example.

FIG. 1 shows the schematic side view of a piezoelectric component;

FIG. 2 shows partial pressures of differing systems;

FIG. 3 shows a detail of an X-ray diffractogram; and

FIGS. 4a-4c show diagrams of grain microstructures in piezoelectricceramics.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a schematic side view of a piezoelectric component in theform of a multilayer component, as a piezoactuator. The component has astack 1 of piezoelectric ceramic layers 10, disposed one atop another,with internal electrodes 20 between them. The internal electrodes 20 aredesigned as electrode layers. The piezoelectric ceramic layers 10 andthe internal electrodes 20 are disposed one atop another.

In the embodiment shown here, the external electrodes 30 are disposed onopposite side faces of the stack 1, and run in stripe form along thestack direction. The external electrodes 30 comprise, for example, Ag orCu and may be applied to the stack 1 as a metal paste, and baked.

The internal electrodes 20 run along the stack direction in alternationup to one of the external electrodes 30, with spacing from the secondexternal electrode 30. In this way, the external electrodes 30 areelectrically connected in alternation with the internal electrodes 20along the stack direction. For producing the electrical connection, aconnection element (not shown here) may be applied to the externalelectrodes 30, by soldering, for example.

The internal electrodes 20 are internal Cu electrodes. The piezoelectricceramic layers comprisePb_(1-x-y-[(2a-b)/2]-p/2)V_([(2a-b)/2-p/2])″Cu_(p)Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃material for which: 0≤x≤0.035, 0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009,0.009≤b≤0.0011, 2a>b, p≤2a-b, RE is a rare earth metal, and V″ is a Pbvacancy. For example, the piezoelectric ceramic layers comprise thematerialPb_(0.9451)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃.

The aim of the working example below is to elucidate the production ofthe component comprising the materialPb_(0.9451)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃.

In accordance with the general formulaPb_(1-x-y-(2a-b)/2)V_((2a-b)/2)″Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃,the parameters x=0.0295, y=0.0211, z=0.475, a=0.00753, b=0.0095, andRE=Yb are selected, resulting inPb_(0.9466)V_(0.00278)″Ba_(0.295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃.First of all, the raw materials Pb₃O₄, TiO₂, ZrO₂, WO₃, Yb₂O₃, BaCO₃,and SrCO₃, whose impurities content has been checked and whose metalcontent determined separately in each case, are weighed out in thecorresponding molar ratio and subjected to rotary mixing with ZrO₂grinding media in an aqueous slip for 24 hours (method step A1).Following evaporation and sieving, reaction takes place at 925° C., witha hold time of 2 hours, in a ZrO₂ capsule, and the reaction product issubjected to milling in an eccentric mill with addition of water, usingZrO₂ beads (diameter 2 mm) (method step A). At 300 cycl/min, a firstaverage diameter d₅₀ of 0.66 μm (corresponding to d₉₀=1.64 μm) isobtained after just 30 minutes. The slip is evaporated down, the residueis passed through a sieve, and reaction takes place a second time, witha 2 h hold time at 950° C., in order to complete the reaction (methodstep A3).

FIG. 3 shows as a detail of an X-ray diffractogram, in which the angle λin ° is plotted against the intensity Int, the comparison between thefirst and second calcination steps, in other words between the productsafter method step A2) and after method step A3). After the firstreaction (plot I) there are still relatively Ti-rich tetragonalparticles present alongside relatively Zr-rich rhombohedralcrystallites, as evident from a splitting of the 200/002 reflection.After the second reaction (plot II), the splitting can no longer beresolved, evidencing the improved uniform distribution of Ti and Zr inthe lattice of the PZT perovskite structure.

Following the addition of 2.5 mol % of PbO in the form of Pb₃)O₄, thereaction powder obtained at 950° C. is subjected to fine milling to 0.3to 0.35 μm in an eccentric mill in water or ethanol, using ZrO₂ beads(diameter 0.8 mm) (method step B). This requires about 2 hours at 300cycl/min. The dispersing medium is evaporated off, and the residue ispassed through a sieve and, following addition of a PEG binder(polyethylene glycol), granules are prepared, from which slices with adiameter of 15.5 mm and a thickness of 1.4 to 1.5 mm arecompression-molded.

Prior to sintering, these green bodies are provided with Cu electrodesby sputtering (method step C).

The compression moldings in slice form are first of all debindered byheating to 500° C. in air, and then sintered with a heating ramp of 6K/min at 1000° C. and with a hold time of 3 h (method step D,comparative sample 1). Further compression moldings are sintered withthe same debindering and heating ramp at 950° C. with a hold time of 4 h(comparison sample 2). Further compression moldings are sintered in anatmosphere with reduced oxygen partial pressure, settemperature-dependently through the ratio of steam to forming gas onheating at 3 K/min, with a hold time at 1010° C. of 4 h (workingexample).

FIG. 2 additionally shows different partial pressures according to whichthe appropriate oxygen partial pressure can be selected as a function oftemperature. In the graph, the temperature T in K is plotted against thelogarithmic oxygen partial pressure log (p(O₂)). The equilibrium partialpressure of the Cu/Cu₂O system, P_(Cu/Cu2O), and of the PbO/Pb system,P_(PbO/Pb), are shown. The oxygen partial pressure P_(O2) is allowed tovary between these equilibrium partial pressures if oxidation of Cu toCu₂O and reduction of PbO to Pb (or of PbTiO₃ to Pb and TiO₂) are to beavoided. FIG. 2 shows one possible profile of the oxygen partialpressure, which throughout the sintering operation lies between theequilibrium partial pressures P_(Cu/Cu2O) and P_(PbO/Pb). This profilehas discontinuities at 940 K and at 1170 K. The discontinuities aresituated between three lines, likewise shown in FIG. 2, which correspondto different amounts of forming gas (line with small dots, line withsmall squares, line with gaps). If the amounts of N₂ and of the H₂Ovapor remain constant, the oxygen partial pressure during sintering canbe adjusted by adjusting the amount of forming gas.

Even under the defined operating conditions of the working example,sintering is accompanied by contamination of Cu from the electrodes, inthe range of about 600 ppm. The Cu cations in the I oxidation state areincorporated as Cu acceptors, with elimination of an equivalent amountof 0.0015 mol of PbO, thus giving the following formula for the finalcomposition of a piezoceramic produced under these conditions:Pb_(0.9451)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃.

The sintered density of the samples in slice form is determined byweighing and ascertaining the geometric dimensions on five individualsamples in each case, and the relative density ρ_(rel) is calculated bycomparison with the X-ray density of the PZT perovskite phase, atρ_(th)=8.03 g/cm³. For the samples provided with 2.5 mol % of PbO assintering aid, after sintering at 1000° C., a density ρ=7.83±0.04 g/cm³is found, corresponding to 97.5% of the theoretical density, and even onsintering at 950° C. a comparable value ρ=8.81±0.04 g/cm³ is obtained,corresponding to 97.3% of the theoretical density. The sinter densityobtained under defined operating conditions is 7.7 to 7.9 g/cm³. In theabsence of addition of PbO in the form of Pb₃O₄, the value ρ_(rel) foundfor the relative density of the sintering at 1000° C. is only 84.9%.

Accordingly, the free specific surface energy introduced by finemilling, and the formation of sinter-promoting defects induced bydonor-acceptor doping at the B sites, are not sufficient to allow highsinter densification at just 1000° C. The addition of 2.5 mol % of PbOin the form of Pb₃O₄ as a sintering aid proves necessary in order toobtain a sufficiently dense piezoceramic.

FIG. 4 shows diagrams of grain microstructures of piezoelectricceramics. FIG. 4a ) shows the microstructure obtained on sintering at1010° C. when the oxygen partial pressure corresponds, on atemperature-dependent basis, during the hold time of 4 h, to the profileshown in FIG. 2. The effect of the as a result of the additionalincorporation of the Cu acceptor centers on grain growth is clearlyapparent. The average grain diameter is 2 to 3 μm. In contrast, thegrain microstructures shown in FIGS. 4 b) and 4 c) for comparativesamples 1 and 2 (sintering in air at 1000° C. for 3 h and sintering inair at 950° C. for 4 h, respectively) show smaller average graindiameters of 1 to 2.5 μm (FIG. 4b ) and 0.5 to 2 μm (FIG. 4c ).

Other characteristic variables of the compression molding according tothe working example, provided with Cu electrodes, are indicatedhereinafter: The deflection parameter d₃₃, which corresponds to thepiezoelectric charge constant, can be defined by the relation S₃=d₃₃*E₃,with the relative extension S=Δl/l and the electric field strength E.The measurement performed after polarization at about 3 kV/mm gives ad₃₃ of 520 pm/V. From a measurement of capacity, the value found for thedielectric constant ε is 2100. For the planar coupling factor, the valuek_(p)=0.65 was ascertained in accordance with the following relation:

$k_{p} \cong {\left\lbrack {{2.51\frac{f_{a} - f_{g}}{f_{a}}} - \left( \frac{f_{a} - f_{g}}{f_{a}} \right)^{2}} \right\rbrack^{1\text{/}2}.}$

The invention is not restricted by the description with reference to theworking examples; instead, the invention encompasses every new featureand every combination of features, including more particularly everycombination of features in the claims, even if this feature or thiscombination itself is not explicitly stated in the claims or workingexamples.

What is claimed is:
 1. A method for producing a piezoelectric component,the method comprising: producing a ceramic precursor material of thegeneral formulaPb_(1-x-y-(2a-b)/2)V_((2a-b)/2)″Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃,where RE is a rare earth metal and V″ is a Pb vacancy; mixing theceramic precursor material with a sintering aid; forming a stack whichincludes alternating layers comprising the ceramic precursor materialand a layer comprising Cu; and debindering and sintering the stackthereby forming the piezoelectric component having Cu electrodes and atleast one piezoelectric ceramic layer comprisingPb_(1-x-y-[(2a-b)/2]-p/2)V_([(2a-b)/2-p/2])″Cu_(p)Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃,where 0≤x≤0.035, 0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009, 0.009≤b≤0.011,and 2a>b, p≤2a-b.
 2. The method according to claim 1, wherein producingthe ceramic precursor material comprises: providing a mixture ofstarting materials, the mixture of starting materials are selected fromthe group consisting of Pb₃O₄, TiO₂, ZrO₂, WO₃, RE₂O₃, BaCO₃ and SrCO₃;calcining the mixture at a first temperature and milling the mixture toa first average diameter; and calcining the mixture at a secondtemperature that is higher than the first temperature.
 3. The methodaccording to claim 2, wherein the mixture obtained by mixing the ceramicprecursor material with the sintering aid is milled to a second averagediameter that is smaller than the first average diameter.
 4. The methodaccording to claim 3, wherein the mixture obtained by mixing the ceramicprecursor material with the sintering aid further comprises adding Cu₂Owith a fraction of 0.05 to 0.1 mol %.
 5. The method according to claim1, wherein mixing the ceramic precursor material comprises adding PbO orPb₃O₄ as the sintering aid, a fraction selected for the sintering aidbeing between 0.5 and 3 mol %, based on 1 mol of ceramic precursormaterial.
 6. The method according to claim 1, wherein forming the stackcomprises applying Cu to the layer comprising the ceramic precursormaterial by sputter-coating with Cu or printing with a Cu paste.
 7. Themethod according to claim 1, wherein debindering the stack takes placeunder steam with exclusion of oxygen.
 8. The method according to claim1, wherein sintering the stack takes place at an oxygen partial pressurewhich lies between an equilibrium partial pressure of PbO/Pb and anequilibrium partial pressure of Cu/Cu₂O.
 9. The method according toclaim 8, wherein the oxygen partial pressure is set by a mixture ofsteam and forming gas.
 10. The method according to claim 1, whereinsintering takes place at a temperature between 1000° C. and 1050° C. 11.The method according to claim 1, wherein x=0.0295, y=0.0211, z=0.475,a=0.00753, b=0.0095, and RE=Yb are selected, and wherein debindering andsintering the stack comprises producing a piezoelectric ceramic layercomprisingPb_(0.945)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃.12. A method for producing a piezoelectric component, the methodcomprising: providing a mixture of starting materials, the mixture ofstarting materials are selected from the group consisting of Pb₃O₄,TiO₂, ZrO₂, WO₃, RE₂O₃, BaCO₃ and SrCO₃; calcining the mixture at afirst temperature and milling the calcinated mixture to a first averagediameter; calcining the calcinated mixture at a second temperature thatis higher than the first temperature and forming a green body; forming ametal layer on the green body; forming a stack of green bodies and metallayers; debindering the stack; and sintering the stack thereby formingthe piezoelectric component with piezoelectric ceramic layers comprisingPb_(1-x-y-[(2a-b)/2]-p/2)V_([(2a-b)/2-p/2])″Cu_(p)Ba_(x)Sr_(y)[(Ti_(z)Zr_(1-z))_(1-a-b)W_(a)RE_(b)]O₃,where RE is a rare earth metal and V″ is a Pb vacancy, where 0≤x≤0.035,0≤y≤0.025, 0.42≤z≤0.5, 0.0045≤a≤0.009, 0.009≤b≤0.011, 2a>b and p≤2a-b.13. The method according to claim 12, wherein forming the metal layercomprises sputtering the metal layer.
 14. The method according to claim12, wherein the metal layer comprises a Cu layer.
 15. The methodaccording to claim 12, further comprising mixing the mixture calcinatedat the first temperature with a sintering aid.
 16. The method accordingto claim 15, wherein mixing the mixture calcinated at the firsttemperature with the sintering aid comprises adding PbO or Pb₃O₄. 17.The method according to claim 15, further comprising milling a mixtureobtained by mixing the mixture calcinated at the first temperature withthe sintering aid to a second average diameter that is smaller than thefirst average diameter.
 18. The method according to claim 12, whereindebindering the stack comprises steaming the stack with exclusion ofoxygen.
 19. The method according to claim 12, wherein sinteringcomprises heating the stack to a temperature between 1000° C. and 1050°C.
 20. The method according to claim 12, wherein debindering andsintering the stack comprises producing the piezoelectric componentcomprisingPb_(0.9451)V_(0.00128)″Cu_(0.003)Ba_(0.0295)Sr_(0.0211)[Ti_(0.467)Zr_(0.516)W_(0.00753)Yb_(0.0095)]O₃.